P21 alternatives.

9 compounds compared to P21, ranked by published evidence tier and regulatory status, not by what's marketed hardest.

Why people look for an alternative

P21 is a synthetic peptide modeled on an active region of ciliary neurotrophic factor, designed to be orally active and to cross the blood-brain barrier. It has been studied in animal models of Alzheimer's disease and Down syndrome, and that is where it stops: it has not been tested in humans, is not approved by any regulatory authority, and exists only as a preclinical research compound. People search for alternatives when they realize the animal results have no human counterpart. The honest answer is that there is no better-evidenced compound acting through this neurotrophic mechanism. The alternatives listed share a category with P21, not a completed clinical program.

What you're comparing against
P21
F tier · 22/100Research / preclinical

P21 (also written P021) is a small synthetic peptide derivative modeled on a biologically active region of ciliary neurotrophic factor (CNTF).

Ranked by evidence · strongest first
  1. 01
    Cerebrolysin
    C tierResearch / preclinical
    porcine brain peptide preparation

    Acts through the neurotrophic factor signalling pathway, like P21. Research / preclinical.

  2. 02
    Semax
    D tierResearch / preclinical

    Acts through the neurotrophic factor signalling pathway, like P21. Research / preclinical.

  3. 03
    Cortexin
    D tierResearch / preclinical
    cattle brain polypeptides

    Acts through the neurotrophic factor signalling pathway, like P21. Research / preclinical.

  4. 04
    N-Acetyl Semax Amidate
    F tierResearch / preclinical

    Acts through the neurotrophic factor signalling pathway, like P21. Research / preclinical.

  5. 05
    Dihexa
    F tierResearch / preclinical

    Acts through the neurotrophic factor signalling pathway, like P21. Research / preclinical.

  6. 06
    Selank
    D tierResearch / preclinical

    Same category: cognition & mood. Research / preclinical.

  7. 07
    PE-22-28
    F tierResearch / preclinical
    spadin analog

    Same category: cognition & mood. Research / preclinical.

  8. 08
    DSIP
    F tierResearch / preclinical
    delta sleep-inducing peptide

    Same category: cognition & mood. Research / preclinical.

  9. 09
    Pinealon
    F tierResearch / preclinical

    Same category: cognition & mood. Research / preclinical.

How this list is built

An “alternative” here means a compound that shares P21's mechanism pathway or sits in the same category, not a marketing substitute. Each is ordered by PepCue's evidence tier (a weighted 0–100 score across human data, safety, replication and regulatory clarity), then by whether it's actually approved. This is a research reference, not medical or purchasing advice: an alternative sitting higher on evidence does not mean it's right, safe, or legal for any given use. Reviewed June 1, 2026.

Comparing options with your provider?

PepCue keeps every compound, dose and lab in one private, provider-ready timeline, whichever one you land on.

Educational and research reference only. Not medical advice, diagnosis, or dosing guidance. Flag an error on this page
Compounds